The present invention relates to a method and apparatus for driving a heat-sensitive recording head with a continuous heat generating element which is employed in a facsimile printer or the like.
In a conventional heat-sensitive recording head of this general type, especially one intended for line scanning, the driving leads correspond to the recording positions in the ratio of 1:1. Because of this, conventional heat-sensitive recording heads suffer from a difficulty that, where it is required to form a record of high quality with a high recording density, the distance between adjacent leads must unavoidably be made small which makes it difficult to connect the leads to the driving circuit.
In order to overcome this difficulty, a recording head with alternately arranged leads as shown in FIG. 1 has been proposed in the art. The recording head, as shown in FIG. 1, includes a heat-resistant and electrically insulated substrate 1, which provides a suitable heat sink effect and which may be a ceramic plate or which may be formed by providing a heat sink on a ceramic plate, and an assembly of heat generating elements 2 arranged in a line, each corresponding to a recording position. The assembly is formed with a thin film, thick film or semiconductor technique. The surface of the assembly of heat generating elements 2 is covered with a protective layer of glass or the like in order to improve the wear-resistance thereof. The recording head further includes a group 3 of source side leads a.sub.1 through a.sub.n and a group 4 of sink side leads b.sub.1 through b.sub.n which are adapted to supply current to the heat generating elements 2. The leads a.sub.1 through a.sub.n and b.sub.1 through b.sub.n are arranged alternately on both sides of the assembly of heat generating elements 2 in such a manner that they segregate the heat generating elements 2 from one another according to the required recording density.
A heat-sensitive recording head of this type has a number of alternate leads which serve as common leads for adjacent recording positions. Therefore, the recording head is advantageous in that the distance between adjacent leads which are connected to the drive circuit can be increased to twice the recording density and the alignment of the leads with the heat generating elements can be readily achieved. However, the recording head cannot be driven with a conventional heat-sensitive recording head driving device because the leads merely segregate the heat generating elements do not correspond to the recording positions in the ratio of 1:1.
FIG. 2 shows an example of a drive circuit for the alternate lead type recording head shown in FIG. 1. In FIG. 2, reference numeral 31 designates a single-line memory for storing one line of data A to be recorded and 32 and 33 designate half-line memories, respectively. The bit data stored in the single-line memory 31 is divided every two adjacent bits to form two groups of data. The two groups of data thus formed are stored in the half-line memories 32 and 33, respectively. Further in FIG. 2, reference numeral 34 designates a change-over switch, 35 the heat-sensitive recording head shown in FIG. 1 and 36 a switch for selecting between common terminals 37 and 38 which are connected, respectively, to a group of odd-numbered sink-side leads of the recording head and to a group of even-numbered sink-side leads. The half-line memory 33 is of a series-input parallel-output type. Its output is connected to the source-side leads of the recording head 35.
In operation, first one line of data A is stored in the memory 31. The data stored is then divided into a first group of data bits (for instance the 1st, 2nd, 5th, 6th, 9th, 10th, . . . bits) and a second group of data bits (for instance the 3rd, 4th, 7th, 8th, 11th, 12th, . . . bits) which are stored in the half-line memories 32 and 33, respectively. Then, the contents of the half-line memory 33 are supplied to the source-side leads of the recording head 35. In this operation, with the selecting switch 36 operated to suitably select between the common terminals 37 and 38, recording is carried out every two adjacent bits. After this operation has been completed, the switch 34 is operated to transfer the contents of the half-line memory 32 to the half-line memory 33. The output signal of the memory 33 is applied to the recording head 35 and the switch 36 is operated similarly as in the above-described case to record one line of data.
The above-described method and circuit are disadvantageous in that, even if a matrix arrangement is employed to reduce the amount of data handled at a time, it is necessary to provide a data distribution circuit with a number of elements, a number of control signals must be used and the necessary timing is complicated. Therefore, the prior art device and method are uneconomical and low in reliability.
Accordingly, an object of the invention is to provide a method and device for driving a heat-sensitive recording head in which all of the above-described difficulties accompanying a conventional driving method have been eliminated and in which the recording head can be driven satisfactorily with a circuit having an extremely small number of components.